Result of eating too much beef? (9)
I believe the answer is:
bellyache
This clue is a double definition.
'result of eating too much' is the first definition.
(overeating might cause a stomach ache)
'beef?' is the second definition.
('bellyache' can be a synonym of 'beef')
(Other definitions for bellyache that I've seen before include "complain" , "Beef" , "Gut pain" , "Moan noisily" , "Gripe" .)